Check this Old Mopar Alternator Tech Video
The most complete set of MTSC up to the mid '70s is collected here:
Master Technician Service Conference - Chrysler's Training for Mechanics
Mymopar has some more of the later ones in a different format (pdfs instead images). They also have some digitized Service manuals for download. if you want bette quality or paper, then Bishko is a decent retailer.
It’s just your average universal unit. This one is branded SCHUMACHER ive seen them branded by many different names All look the same internally. I’ve bought and used one before on one of my past vehicles.
OK. Lets look at the instructions.
https://www.batterychargers.com/sites/default/files/manuals/0099001450-R2.pdf
It's basically a voltmeter with a fixed resistance that can be turned on to load the battery.
Take a quick Rough reading this way I was suggested if I couldn’t figure out the alternator. All my checks were at idle around 1000-1200 rpm
There's usually a big difference in power generation between idle (650 to 950 on a few cars) and 1250 rpm. The instructions for that tester say 1200 to 1500 rpm in general. So you can see its not just Chrysler's alternators. I'll come back to this.
I believe this might be the case or some other stock power supply but it ran like this for years before me owning and almost 2 years of my ownership no problems.
I beleive you. So the question is whether its battery, alternator, or a wiring issue. Wiring issues could be a poor connection from the alternator feed choking the flow of higher currents, or a something that is causing additional current draw. One cause of additional current draw would be a run down battery. So that is definately the first test to test. The question is not whether the battery has lots of power, but whether its fully charged. A crude check is after starting the car to check the ammeter for when its done charging.
Alternator:
Alternators are very rpm dependent.
Here's the max output specs for a GM 12Si with the engine rpm for my jeep (which uses this alternator).
All alternators have max output curves something like this.
Power is P = IV so take 667 engine rpm, the '94 amp' alternator can produce up to 50 amps x 12 v = 60 Watts.
When tested at higher voltage, the current will be lower.
So.
Make sure the belt is snug.
Make sure the battery is done recharging. (use the car's ammeter to check)
Then start putting load on it per the instructions.
Note that they do
not suggest using the tester's internal load. They suggest turning on the lights and heater fan.